Process for desulfurizing coke

ABSTRACT

Petroleum coke of reduced sulfur content is produced by adding an alkali metal carbonate (preferably sodium carbonate) to the coker feedstock prior to coking and then, after coking, treating the coke with hydrogen at an elevated temperature.

United States Patent 11 1 Related U.S. Application Data Continuation-in-part of Ser. No. 799,150, Feb. 10, 1969, abandoned.

U.S. Cl. ..208/46, 208/131, 201/17 Int. Cl ..Cl0g 9/14, ClOb 57/00 Field of Search ...208/46, 106, 127, 131; 201/17 s RECYCLE H 4 Thakker 1 1 Mar. 27, 1973 [54] PROCESS FOR DESULFURIZING COKE [56] References Cited 75 Inventor: Mahendra T. Thakker, Ponca City, UNITED STATES PATENTS Okla- 2,921,017 1/1960 Johnson et al ..208/106 2,721,169 10 1955 Mason et al ..23 209.9 [7'3] Ass'gnee' ga g f z Company. 2,872,384 2 1959 Nelson et a] ..201 17 3,009,781 11/1961 Johnson et al... .....201 17 [22] Filed: Apr. 16, 1971 3,179,584 4/1965 Hamner et aL. .208/106 [21] Appl. No.: 134,909

Primary Examiner-l-lerbert Levine Att0rneyJoseph C. Kotarski et al.

[57] ABSTRACT Petroleum coke of reduced sulfur content is produced by adding an alkali metal carbonate (preferably sodium carbonate) to the coker feedstock prior to coking and then, after coking, treating the coke with hydrogen at an elevated temperature.

7 Claims, 1 Drawing Figure SCRUBBER CRUSHER qcPARATOn TO CALCINER DESULFURIZER WASH WATER COKER FEEDSTOCK 0V ERHEAD MIXER GREEN COKE DELAYED COKER 8 RECYCLE H2 Tf 0: U u CRUSHER 'sEPARAToRi 5 (D s 4 g H01" WATER WASHER 9 1 lo To WASH CALCINER WATER INVENTOR MAHENDRA r THAKKER ATTORNEY PROCESS FOR DESULFURIZING COKE CROSS-REFERENCE TO RELATED APPLICATIONS This application relates to my application Ser. No. 799,151 entitled PROCESS FOR DESULFURIZING COKE filed Feb. 10, 1969 and is a continuation-inpart of Ser. No. 799,150 filed Feb. 10, 1969 and both now abandoned.

BACKGROUND This invention is a process for producing coke of reduced sulfur content by adding an alkali metal carbonate (or mixtures of such carbonates) to the coker feedstock and then, after coking, treating the coke with hydrogen at an elevated temperature.

The importance of coke desulfurization processes will undoubtedly increase as air pollution regulations result in the establishment of coke specifications including lower sulfur contents. The problem is accentuated by the present trend toward the use of higher sulfur content crude oils in many oil refineries.

One method of reducing the sulfur content of a coke is to reduce the sulfur content of the feed to the coker, either by careful selection of feedstocks or by desulfurization of the feedstock. Another method involves the desulfurization of the coke itself. This invention concerns the latter alternative.

DESCRIPTION OF THE PRIOR ART The prior art suggests methods of desulfurizing petroleum coke by the addition of sodium carbonate to the coke, followed by heat treatment. For example, see the following references: Ind. Eng. Chem., Vol. 52, No. 8, pp 675-677 (1960); US. Pat. No. 3,387,941.

US. Pat. No. 3,179,584 shows addition of sodium carbonate to coker feedstock to increase the production of hydrogen in the coking process, but desulfurization is not disclosed or suggested.

US. Pat. No. 2,921,017 suggests mixing sodium carbonate with a coker feedstock in order to produce a coke of reduced sulfur content; however, the patentee does not disclose the use of hydrogen.

The prior art also suggests desulfurization of coke by hydrogenation, as for example: US. Pat. No.

3,130,133; Ind. Eng. Chem., Vol. 52, No. 7, pp

599-600 (1960); US. Pat. No. 2,768,939.

The prior art also shows the desulfurization of coke by treatment with hydrogen in the presence of materials other than sodium carbonate, e.g.: US. Pat. Nos. 2,824,047 and 3,101,303.

The prior art also teaches that petroleum fractions generally can be used for coking feedstocks. The prior art also has recognized that certain reduced crudes, thermal tars including tars from ethylene and other olefin processes are superior as feedstocks when a needle like or premium coke is desired. While the art recognizes that any hydrocarbon can be used as a coking feedstock, the lower molecular weight materials generally are more valuable for other purposes and the heavy resids and tars, having a high carbon content are more suitable and are more easily coked. The choice of feedstocks then depends upon economies and type of coke desired, the choice being within the skill of the art.

BRIEF SUMMARY OF THE INVENTION This invention is a process for producing coke of reduced sulfur content by adding an alkali metal carbonate (or a mixture of such carbonates) to the coker feedstock and then, after coking, treating the coke with hydrogen at an elevated temperature. Sodium carbonate is preferred because it is cheap, although other alkali metal carbonates could be used.

Sodium carbonate is mixed directly with the coker feedstock and the feedstock is then coked. After the coking operation is completed, the coke is ground to a particle size sufficiently small that the hydrogenation treatment will be effective, and preferably sufficiently small so that the coke can be fluidized during hydrogenation.

After the hydrogenation step, the coke is washed with water in order to remove the carbonate.

DESCRIPTION OF THE DRAWING The drawing shows a simplified flow diagram illustrating the process.

DETAILED DESCRIPTION OF THE DRAWING Referring to the drawing, a suitable conventional coking feedstock is passed to mixer 1, in which sodium carbonate is blended into the feedstock. The resulting mixture is passed to coker 2 (for example, a conventional delayed coker) which is operated under conventional coking conditions. The green coke is ground in crusher 3 to a particle size of less than 12 US. Standard mesh, preferably -50 to +100 Standard U.S. mesh. The particles of greater than 12 mesh are separated into separator 4 and recycled to the crusher. The ground coke is then conveyed to desulfurizer 5, into which hydrogen is introduced through line 6. The desulfurizer is preferably operated so as to maintain the coke bed in a fluidized condition. The overhead vapors are passed through a conventional H S scrubber 7 from which recycle hydrogen is recovered through line 8. The desulfurized coke, after washing with hot water in washer 10, may then be passed to a calciner (not 45 shown). The preferred conditions are as follows:

Amount of sodium carbonate (added to coker feedstock): 0.3 to 5 percent, preferably 0.3 to 1 percent, based upon coke obtained (line 9 of drawing), depending upon the amount of sulfur in the coke.

Hydrogenation treatment temperature, F: at least about 1,000F, to about 2,000F, preferably about 1,000 to 1,600F and most preferably about 1,100F to 1,400F.

Hydrogenation pressure, atm: any convenient pressure is satisfactory. Atmospheric pressure is satisfactory although higher pressures are preferable.

Hydrogenation treatment time, hours: at least 2' hours, preferably 3 to 8 hours, and most preferably 4 hours, for low sulfur cokes. For high-sulfur cokes, treating times of up to 16 hours may be required, preferably 8-12 hours.

The particular set of conditions selected will, of course, depend upon the sulfur content of the coker feedstock and the desired degree of sulfur removal. The preferred set of conditions for the hydrogen treatment of low-sulfur feedstocks is a 4-hour treatment at about 1,200F. For high sulfur coke (greater than 2 percent), the treatment time should be increased to obtain the desired reduction in sulfur content.

The process may be carried out as a batch or continuous operation.

In the following tables, the particle sizes refer to US. Standard mesh. The coker feedstock was reduced crude. Table 1 illustrates the effectiveness of this process. in Run No. 1, sodium carbonate was added to the coke, whereas in all other runs, it was added to the coker feedstock.

in all the tables, the final ash content was measured after washing the coke with water.

TABLE I.COKE MADE BY ADDITION F NEMCO: T0 ItEDUCED 013111513 A comparison of runs from the above table with that of Table 11 shows at a given temperature, the improvement in coke removal is substantial. At 1,600F, runs 12 and 20, the improvement was 29.9 percent. However, as we increase temperature, the total sulfur removed becomes less and therefore about 2,000F is a practical upper limit.

it is also pointed out, as is known in the prior art, that the nature of the coking feedstock, or rather the resulting coke, will determine the optimum hydrogenation temperature for desulfurization. With the particular feedstock, e.g., the particular reduced crude, showed an optimum temperature at about 1,200F both with the prior art method and the invention method. With Run number..- 1 2 3 4 5 6 7 8 9 Particle size 50+100 -30+100 30+100 30-1-100 30-1-100 -30+100 -30+100 -30+100 30+100 Percent NazCOs a '4 0 5 4. a7 2. 17 1. 32 0. 034 0. 335 0. 7 Fluidlzing gasm. H2 H2 H2 H2 H2 H2 Hz He H2 Temperature, F 1,200 1, 200 1, 200 1, 200 1, 200 1, 200 1,200 1, 200 1,000 Pressure, atm 1 1 1 1 1 1 1 1 Velocity of gas, ft.lsee 0. 374 0. 373 0. 373 0. 373 0. 373 0. 373 0. 373 0. 373 0. 373 Treatment time, hrs 4 4 1 4 4 4 4 4 4 Initial sulfur, wt. percent. 1. 16 1. 35 1.111 1.11 1. 3 1 1. 36 1. 30 1. 44 1. 36 Initial ash, \vt. percent 0. 2 -1. 07 2. 49 1. 611 0.117 0.1111 0.11 Final sulfur, wt. percent (l. 03 (1. 82 I). '28 0. 32 0. 50 0. 5 0. 711 0. 03 0. 08 Wt. loss on treatment, nereent 14 3. 5 6.0 6.1 1 4. 3 5. 72 1. 31 1. 75 5. 6G lercent sulfur ren1ove 1 56.215 71.17 50.118 133.21 113. 511. 27. J4 Finalash,wt.percent 1.311 7 Li A. i 0.751 11.111) W 0.172 igs Run number 10 ll 11 15 111 17 18 10 Particle s17.o...... -+100 -30+100 30+100 30+100 30-1-100 30+100 -12+30 -4+12 -30+100 -30+100 Percent Nznflt); added. 0. 7 0. 7 0. 7 0. 110 0. 00 0.110 11. 7 0. 7 0. 7 0. 7 1 1u1d1z1np; gas 11: 112 11: He 11: 11 11: 11,1 11; 1: Temperature, F 1, 200 1, 400 1,1100 1, 200 1, 200 1, 200 1, 200 1, 200 1, 200 1, 200 Pressure, atm 1 1 l 1 1 l 1 1 1 1 Velocity of gas, ft./sec. 0. 373 0. 373 0. 373 0. 373 11. 7411 1.12 .373 .373 .373 .373 Treatment time, hrs 4 4 1 4 4 4 4 4 0 8 Initial sulfur, wt. pereent. 1. 30 1. 27 1. 27 1. 31 1. 3-1 1. 30 1. 3 1. 3 1.35 1. Initial ash, wt. percent .71 .71 U. 53 0. 53 Final sulfur, wt. pereent 0. as 0.07 0. 07 0. 55 0. 5t 0. 01 0. s3 .31 0. 53 0. 57 Wt. loss on treatment, percent. 5. 66 5. fl 4. 34 5. 7 5. 23 3. '1 3. 7 3. 43 (1.0 0. 8 Percent sulfur removed 57. 35 47. 24 23. 62 58. J6 50. 7 55. 15 55. 311 37. 611 60. 74 57.78 Final ash, wt. pereent 0. 5 0. 7 0. .1 0. 6 0. 01 0. 57 .54 .011

"Added to coke.

It can be seen that 1f the sodlum carbonate 1s added another crude res1d or some other feedstock, the opto the coker feedstock (rather than to the coke itself as timum could be at 1,400 or 1,600F. The invention in Ser. No. 799,151), equivalent results can be obmethod would show similar improvement but the optained using less sodium carbonate, which is important timum would then be 1,400 or 1,600F, respectively as an ash content of over 1.0 percent is undesirable. As (see Runs 29 and 30). indicated by Run No. 4, a high percentage of sulfur is Treatment of a mixture of sodium carbonate and removed using 5 percent sodium carbonate, but a high coker feedstock with an inert gas such as nitrogen (inash content is obtained. The ash content can be stead of hydrogen), under comparable conditions of reduced, as for example by an acid wash, but such a temperature and time, does not give the degree of treatment is an added expense. This is why I prefer to desulfurization which is obtained when sodium caruse 1 percent or less sodium carbonate (based on coke bonate and the hydrogen treatment is used in acbut added to the coker feedstock). cordance with my process.

Table 111 shows the results of desulfurization of high Table [I sulfur coke using my process.

EFFECT OF TREATMENT WITH HYDROGEN AND NO SODIUM CARBONATE TABLE Run Number 20 21 22 23 DESULFURIZATION OF HIGH SULFUR COKE Particle Size 50+100 50+100 50+100 50+100 Temperature, "F 1600 1400 1200 1000 Run Number Pressure, atm 1 1 1 l 24 25 26 27 28 Hydrogemvelftlsec 0.44 0.44 0.44 0.44 Particle Size Treatment lime, hrs 4 4 4 4 30+1e30+100 30+100 30+100 30+100 ln1t1al sulfur, wt 1.32 1.32 1.32 1.32 N co Add d, Final sulfur, wt 1.08 0.94 0.79 1.29 of coke Initial V.M., wt 8.53 8.53 8.53 8.53 None 0.7 1.4 1.4 0.7 F1nalV.M., wt 1.61 4.16 Temperature, F Loss on treatment, 6 5 1,200 1,200 1,200 1.200 1,200 wt 10.29 11.42 8.57 5.72 Velocity, Ft./Sec sulfur removed 18.18 28.79 40.15 2.27 0.373 0.373 0.373 0.373 0.373

Treatment Time, Hrs.

4 4 4 l2 16 Initial Sulfur, Wt.

4.18 4.38 4.32 4.32 4.8 initial Ash, Wt.

0.2 0.93 0.93 0.67 Final Sulfur, Wt.

2.32 2.15 2.06 1.09 1.14 Final Ash, Wt.

1.22 0.36 0.24 0.88 0.5 Wt. Loss on Treatment 2.86 2.6 5.7 3.96 8.5 Sulfur Removed The process of this invention has the following advantages over the one described in my co-pending application Ser. No. 799,151 (in which sodium carbonate is added to the coke rather than to the coker feedstock).

1. Sodium carbonate is well distributed in the coke because it can be mixed effectively in the liquid phase. This reduces the amount of sodium carbonate required for-the desired sulfur reduction.

2. The ash content of the coke can be maintained at low levels. This is because only a small amount of sodium carbonate is required. The data of Table I show the above two advantages of the process.

The sodium carbonate added to the coker feedstock is distributed in the entire coke. It probably catalyzes the cracking of sulfur compounds in the coke when treated with hydrogen at elevated temperatures. Thus, most of the sulfur comes out as H 8 during the hydrogen treatment step.

Using a different coke prepared from different coker feedstocks, the following results were obtained using the process of the invention. Runs 29 and 30 were on the same coke prepared from a reduced crude, whereas Run 31 was with a coke prepared from a thermal tar.

TABLE IV Run Number 29 30 31 Particle size 50+l00 -50+100 50+l00 Na,C0 added 5.4 5.4 2.85 Temperature, "F 1,200 1,600 1,200 Velocity, Ft/Sec 0.373 0.373 0.373 Time. Hrs. 4 4 4 Initial sulfur, wt 1.27 1.30 0.48

Final sulfur, wt 0.54 0.50 0.12 Wt loss 6.0 5.6 5.72 sulfur removed 57.5 61.5 75.0

From Runs 29 and 30 it can be seen that with this particular coke, the better hydrogenation temperature was 1,600F. Run 31 is included to show the operability of the invention using a different type of feedstock.

What is considered new and inventive in the present invention is defined in the hereunto appended claims, it being understood, of course, that equivalents known to those skilled in the art are to be construed as within the scope of the invention. For example, any conventional coker feedstock, as discussed under Background, may be used. Bicarbonates, sesquicarbonates, or hydrates of carbonates could be used in place of carbonates and are referred to simply as carbonates.

What is claimed is:

A process of producing petroleum coke of reduced sulfur content comprising the steps of adding from about 0.3 to about 5 weight percent of an alkali metal carbonate, based upon coke obtained, to a liquid hydrocarbon coker feedstock, coking the resulting mixture, recovering the coke in a particle size of less than 12 U.S. Standard mesh suitable for fluidizing, and treating in the presence of hydrogen the recovered coke in a fluidized state for at least 2 hours at a temperature of about 1,000 F. to about 2,000 F.

2. The process of claim 1 wherein the coke is subjected to grinding to produce a suitable particle size for hydrogenation.

3. The process of claim 2 wherein the coke is reduced to particle size of less than 12 U.S. Standard mesh.

4. The process of claim 3 wherein the coke is heated at a temperature in the range of about 1,l00 to about 1,600F.

5. The process of claim 4 wherein the coke is washed with water after it is treated with hydrogen.

6. The process of claim 5 wherein the alkali metal carbonate is sodium carbonate.

7. The process of claim 6 wherein the temperature of treating with hydrogen is in the range of about 1,100F to about 1,400F. 

2. The process of claim 1 wherein the coke is subjected to grinding to produce a suitable particle size for hydrogenation.
 3. The process of claim 2 wherein the coke is reduced to particle size of less than 12 U.S. Standard mesh.
 4. The process of claim 3 wherein the coke is heated at a temperature in the range of about 1,100* to about 1,600*F.
 5. The process of claim 4 wherein the coke is washed with water after it is treated with hydrogen.
 6. The process of claim 5 wherein the alkali metal carbonate is sodium carbonate.
 7. The process of claim 6 wherein the temperature of treating with Hydrogen is in the range of about 1,100*F to about 1,400*F. 